Linear actuator

ABSTRACT

A linear actuator is provided with an armature and a stator. The armature has at least two stacks of permanently magnetic rods one over another, the stacks being arranged at a predetermined distance from each other. The stator is at least partly produced from a soft magnetic material, and comprises at least two pairs of teeth with teeth opposite each other, each pair of teeth receiving one of the two stacks between them while forming an air gap. The stator has at least two magnetically conducting inner areas which are located between the two stacks and arranged at a predetermined distance from each other in the direction of motion of the armature. The inner areas are each at least partially surrounded by a substantially hollow cylindrical coil arrangement, the central longitudinal axis of which is oriented substantially transversely to the direction of motion of the armature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of International Patent Application No.PCT/EP2006/002905, filed Mar. 30, 2006.

BACKGROUND OF THE INVENTION

This invention concerns a linear actuator, which is to be operatedelectrically, with a rotor and a stator, the rotor being set up to acton an element which is to be moved.

PRIOR ART

From JP-A-3-92518, a drive device is known, the stator in said drivedevice being constructed of two approximately semi-cylindrical shells,which both in the circumferential direction and in the longitudinaldirection of each shell have divided teeth which face the rotor. Theindividual teeth of each shell are each surrounded by a coil, thecentral longitudinal axis of which runs in the radial direction. Theresult is a magnetic flux which is oriented in the radial direction, andwhich, starting from each one of the multiple teeth, flows into therotor through the air gap between stator and rotor.

A version, which agrees to this extent, of the stator, stator coils androtor of a drive device for a valve arrangement in internal combustionengines is described in U.S. Pat. No. 5,129,369. Here too, stator teethwhich are divided in the radial and tangential directions are eachsurrounded by a coil, the central longitudinal axis of which runs in theradial direction.

EP 0 485 231 A1 too shows a similar type of configuration of the stator,the stator coils and the rotor of a drive device for a valve. Herestator teeth which are divided in the radial and tangential directionsare each surrounded by a radially oriented coil.

These arrangements require very high expenditure in production, sincethe mounting of the coils around the individual teeth is difficult toimplement. The pole pitch which can be achieved with this structure isalso relatively great. A cylindrical element which is fixed to the valvecontains multiple closed secondary coils, which are held in a magneticcore of pressed or sintered magnetic powder without a predeterminedmagnetic orientation.

From DE 10 2004 003 220 A1 (Continental Teves), a valve drive for a gasexchange valve is known, with a magnetic rotor, which extends so that itcan move longitudinally with a rotor section which is remote from thegas exchange valve within a bushing of a stator, which is provided witha current coil. The valve drive has a toothed area which forms a magnetyoke, and with a rotor end, which projects out of the stator in thedirection of the gas exchange valve, said rotor actuating the gas exischange valve when a current coil is excited. In the area of the rotorsection, the rotor is implemented as a rotor plate which is movedvertically in the stator, and in which multiple magnet pieces arealigned in multiple planes. On both sides of the rotor section, pairs ofcurrent coils, the central longitudinal axis of which is orientedparallel to the rotor motion, are arranged. Transversely to the currentcoils, on their faces, stator plates with toothed areas facing the rotorare arranged.

From WO98/55741, an electrical travelling-wave motor having a rotor anda stator is known. The stator is built from metal sheets, the surface ofwhich is oriented vertically to the direction of motion of the rotor.The stator has teeth, which face the rotor, which is in the form of asynchronous or asynchronous rotor, said teeth each having a closedlateral cylinder surface which faces the rotor. Between each pair ofadjacent teeth of the stator, stator coil chambers are formed, and ineach of them a coil, which is oriented parallel to the surface of themetal sheets, is arranged.

From U.S. Pat. No. 6,039,014, a linear motor is known. In this case astator of the linear motor has multiple coils, which are each separatedfrom each other by a ferromagnetic housing section. A rotor isconstructed from multiple sections consisting of a permanently magneticmaterial, sections consisting of a ferromagnetic material being arrangedbetween them.

Further documents showing the technical background of the invention are,without claiming completeness: DE 33 07 070 A1, DE 35 00 530 A1, EP 244878 B1, WO 90/07635, U.S. Pat. No. 4,829,947, EP 377 244 B1, EP 347 211B1, EP 390 519 B1, EP 328 194 B1, EP 377 251 B1, EP 312 216 B1, U.S.Pat. No. 4,967,702, U.S. Pat. No. 3,853,102, DE 10 2004 003220 A1, U.S.Pat. No. 4,829,947, U.S. Pat. No. 4,915,015, WO 90/07637, EP 244 878 B1,EP 328 195 A2.

PROBLEM ON WHICH THE INVENTION IS BASED

All designs which are described in the above-mentioned documents have incommon that with them the lifting, pushing and dynamics, which arerequired for many application areas, are not achieved with sufficientlycompact construction and high reliability. Additionally, knownarrangements are very cost-intensive in production, and require a lot ofspace.

SOLUTION ACCORDING TO THE INVENTION

To remove these disadvantages, the invention teaches a linear actuatorwhich is defined by the features of claim 1.

Structure, Further Developments and Advantages of the Solution Accordingto the Invention

According to the invention, the linear actuator has a rotor and astator. The stator is at least partly formed of a soft magneticmaterial, and has at least one pair of teeth with teeth opposite eachother, each pair of teeth receiving a stack between them, forming an airgap. The stator has at least two magnetically conducting inner areas,which at their ends facing the rotor have at least one of the teeth, andwhich are arranged at a predetermined distance from each other in thedirection of motion of the rotor. The inner areas are at least partiallysurrounded by a substantially hollow cylindrical coil arrangement, thecentral longitudinal axis of which is oriented approximatelytransversely to the direction of motion of the rotor. In its simplestversion, the rotor has a stack of permanently magnetic rods which arearranged one above another. Laterally next to it, on one side of therotor, the coil arrangement of the stator and the at least twomagnetically conducting inner areas which are surrounded by the coilarrangements is arranged, the rotor having at least one stack ofpermanently magnetic rods which are arranged one above another, andadjacent rods of a stack having an alternating magnetic orientation,which is essentially is aligned with the central longitudinal axis oftwo opposite teeth of a tooth pair.

The invention has recognised that in the case of such an arrangement,the two coil arrangements can be operated so that the magnetic fluxthrough one of the two magnetically conducting inner areas is at everyinstant essentially equal and opposite is to the magnetic flux throughthe other magnetically conducting inner area. Thus the total arrangementof the two coil arrangements with the associated stator arrangement, ininteraction with the permanently magnetic rotor rods, forms aself-enclosed magnetic circuit. In other words, with the invention, themagnetic flux which is induced by one coil arrangement in one directioncan be simultaneously induced by the other coil arrangement in the otherdirection, so that the circuit is closed.

According to the invention, the rotor can have two or more stacks ofpermanently magnetic rods which are arranged at a predetermined distancefrom each other, and the magnetically conducting inner areas of thestator can be arranged between the stacks of the rotor.

Another concept on which the invention is based consists of “separatingout” that part of the stator which effects the armature magnetomotiveforce, namely the coil area with the stator coil arrangement, spatiallyfrom the part which forms the force of the linear actuator, namely thetoothed area of the stator. Thus, in comparison with traditional linearmotors, in which the stator coils are each arranged between two teeth ofthe stator, a considerably higher armature magnetomotive force can beachieved. This is because the coil, because of the form according to theinvention, has considerably fewer spatial restrictions, and can thus beoptimised to minimum (ohmic) losses, and associated maximum magneticflux induction. The arrangement of the stator coil arrangement, thecentral longitudinal axis of which is oriented transversely to thedirection of motion of the rotor, or in other words is essentiallyaligned with the central longitudinal axis of two opposite teeth of atooth pair, is magnetically specially efficient, because the magneticflux which is induced by a coil in such an orientation flows equallythrough the tooth pairs on the two faces of the coil. Thus acorresponding force is generated in both stacks of permanently magneticrods. With no other special steps, this prevents the rotor running skew.

The invention also provides that the hollow cylindrical coil arrangementhas an essentially rectangular cross-section when seen along its centrallongitudinal axis M. Thus a coil, the outer contour of which isessentially rectangular, with a recess which is also essentiallyrectangular, encloses the appropriate magnetically conducting innerareas of the stator.

The dimensions of the permanently magnetic rods in the direction ofmotion of the rotor, and the dimensions of a tooth of the stator in thedirection of motion of the rotor, define a pole pitch which is smallerthan the measurement of the stator coil in its longitudinal direction.

Similarly, the rotor magnetic pole/stator tooth arrangements, whichcause the force and movement, are concentrated, so that they are notinterrupted by stator coil arrangements. This allows a very small polepitch, which in turn causes a high force density. Additionally, with thearrangement according to the invention, partial liftings of the rotorare possible.

Another essential advantage of the linear actuator according to theinvention is that practically only the magnetically active components(the permanent magnets) contribute to the inert mass of the rotor,whereas all other parts of the motor (coils, magnetic return path, etc.)are assigned to the stator. In this way, a specially high ratio of forceexerted by the actuator to inert mass can be achieved.

Because of the arrangement (single-phase and hollow cylindrical, e.g.rectangular in cross-section), which can be simply formed, of the statorcoil arrangements, it is possible to keep the effect of the jarringforces acting on the coil low, so that vibrations of the coil orfriction of the coil on the wall of the stator coil chamber are small.It is thus possible to manage with minimum insulation material andlining material of the stator coil chamber. This too contributes to thecompactness and reliability of the is total arrangement. Additionally,the simple structure results in a high power density even in the case ofsmall linear actuators, since the achievable fill factor of the statorcoil chamber (coil volume in the stator coil chamber relative to thetotal volume of the stator coil chamber) is high.

According to the invention, each tooth can have, in the direction ofmotion of the rotor, a measurement which essentially agrees with themeasurement of a permanently magnetic rod in the direction of motion ofthe rotor, so that in a predetermined position of the rotor, at leastone tooth pair of the stator is aligned with at least one permanentlymagnetic rod.

Preferably, in the direction of motion of the rotor, adjacent toothpairs of the stator are dimensioned, relative to the measurement of thepermanently magnetic rods in the direction of motion of the rotor, sothat between two permanently magnetic rods, which are aligned with twomutually adjacent tooth pairs of the stator, at least one other of thepermanently magnetic rods is arranged.

According to the invention, the magnetically conducting inner areas, attheir ends facing the rotor, can have at least one of the teeth. In thecase of a rotor with two or more stacks, the magnetically conductinginner areas of the stator, between the two stacks, have the teeth attheir ends facing the stacks of the rotor.

In the case of a rotor with two stacks, the stator can also have twomagnetically conducting outer areas which are outside the two stacks ofthe rotor, and which have the teeth at their ends facing the stacks.

According to the invention, the outer area of the stator, at least inone sub-section, is essentially comb-shaped in cross-section. The teethof the comb form the outer teeth of the tooth pairs.

According to the invention, the central longitudinal axis of the coilarrangement can be oriented approximately transversely to the directionof motion of the rotor. Similarly, according to the invention thecentral longitudinal axis of the coil arrangement can be approximatelyaligned with the central longitudinal axis of two mutually oppositeteeth of a tooth pair, or at least in sections be oriented essentiallyparallel to it. This allows a bent shape of the inner areas of thestator, e.g. to obtain corresponding assembly space for the coilarrangements.

The predetermined distance between the two magnetically conducting innerareas can be dimensioned, in conformity with the invention, so that itessentially agrees with the measurement of an even number of permanentlymagnetic rods of the two stacks in the direction of motion of the rotor.

According to the invention, in each case, two adjacent permanentlymagnetic rods of the two stacks of the rotor can be connected to eachother by magnetically inactive spacers, at a predetermined distance.These spacers can contain a magnetically inactive light material(aluminium, titanium, plastic—also with glass fibre or carbon fibreinclusions—or similar). In this way the inert mass of the rotor is low,but its stability is high.

According to the invention, because of the measurements of thepermanently magnetic rods in the direction of motion of the rotor andthe measurements of the teeth of the stator in the direction of motionof the rotor, a pole pitch which is smaller than the measurement of thestator coil arrangement in the direction of motion of the rotor can bedefined.

According to the invention, the outer area(s) of the stator can have, inaddition to or instead of the inner areas of the stator, at least onestator coil.

According to the invention, the measurement of the coil arrangement ofthe stator in the direction of motion of the rotor can be greater thanthe distance between two adjacent tooth pairs of the stator.

Because of the practically exclusively two-dimensional magnetic fluxcourse through the stator, the stator (the inner and/or outermagnetically conducting area) is preferably constructed from electricalsheet parts. However, it is also possible to produce it, at leastpartly, as a soft magnetic mould, preferably of pressed and/or sinteredmetal powder.

According to the invention, the outer areas of the stator at leastpartly form a magnetic return path body,

Because of the high power density of the arrangement according to theinvention, the transverse measurements of the linear actuator, with thenecessary power data, can be kept very small. This allows use inrestricted spaces.

Other features, properties, advantages and possible modifications areexplained on the basis of the following description, which refers to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1, an embodiment of a linear actuator according to the inventionis illustrated schematically in perspective longitudinal view.

In FIG. 2, an embodiment of a coil arrangement of the linear actuatoraccording to the invention is illustrated schematically in perspectiveplan view,

In FIG. 3, an embodiment of a stator of the linear actuator according tothe invention is illustrated schematically in perspective plan view.

In FIG. 4, an embodiment of a stack of magnetic rods of the linearactuator according to the invention is illustrated schematically inperspective plan view.

In FIG. 5, an embodiment of a linear actuator according to the inventionis illustrated schematically in perspective longitudinal view.

DETAILED DESCRIPTION OF THE CURRENTLY PREFERRED EMBODIMENTS

In FIG. 1, a first embodiment of an electrical linear actuator 10, whichhas a rotor 16 and a stator 18 which are connected via a rod 12 a to apart (not illustrated) to be driven, is illustrated. Those skilled inthe art understand that the term “rotor” is used broadly to identify amoving element even though the motion is translational and orrotational. In the following description the rotor 16 translates andreciprocates along its axis.

The rotor 16 has two parallel stacks 14, 14′, which are arranged at adistance L from each other, of multiple permanently magnetic rods 30,30′, which are of essentially cuboidal shape and arranged one aboveanother.

The stator 18 is in the form of a soft magnetic mould of sinteredferrous metal powder or layered iron sheets. The stator 18 has multipletooth pairs 22 a, 22 a′; 22 b, 22 b′; 22 c, 22 c′; 22 d, 22 d′; 22 e, 22e′; 22 f, 22 f with teeth 22 opposite each other. Between the teeth 22of each tooth pair, one of the two stacks 14, 14′ is received, formingan air gap 24 and 24′ respectively.

Between the two stacks 14, 14′ of the rotor 16, the stator 18 hasmagnetically conducting inner areas 50, 50 a, which are arranged at apredetermined distance A from each other in the direction of motion B ofthe rotor 16. Each of the two inner areas 50, 50 a of the stator 18 issurrounded by an essentially hollow cylindrical coil arrangement 60, 60a. The central longitudinal axis M of each of the coil arrangements 60,60 a runs approximately transversely to the direction of motion B of therotor 16. To achieve as high a fill factor as possible, the coilarrangement 60, 60 a is implemented as a copper band coil.

Current must be applied to the two coil arrangements 60, 60 a so thatthey each generate a magnetic field in opposite directions. In FIG. 1,the upper coil arrangement 60, in the shown position of the rotor 16,generates a magnetic field which is essentially oriented from left toright along the central longitudinal axis of the coil arrangement 60,whereas the lower coil arrangement 60 a, in the shown position of therotor 16, generates a magnetic field which is essentially oriented fromright to left along the central longitudinal axis of the coilarrangement 60. This alternates, to is drive the rotor 16 along thedirection of motion B (up or down).

Since each coil arrangement 60, 60 a, over its whole extent, completelysurrounds the appropriate one of the two inner areas 50, 50 a of thestator 18, it can be filled with maximum winding space. As illustratedin FIGS. 1 and 2 by corresponding arrows—or arrow tips and arrowends—current must flow through the two coil arrangements 60, 60 a sothat in the central section 64, in which they are adjacent to eachother, they each carry current in the same direction (see FIG. 2).

In the shown arrangement, the rotor 16 is formed from two stacks 14, 14′which are in parallel alignment, and the magnetic rods of which areformed from permanently magnetic material (e.g. samarium-cobalt). Theindividual magnetic rods 30 are in a flush arrangement one aboveanother, the magnetic orientation of the magnetic rods 30 being alignedalternately (from the inner area of the stator 18 outward and viceversa). Additionally, the dimensions of the magnetic rods 30 are suchthat in a predetermined position of the rotor 16, one of the magneticrods 30 is aligned between two teeth 22 of a tooth pair of the stator18. Adjacent rods 30, 30′ of a stack 14, 14′ have an alternatingmagnetic orientation N->S, S<-N. Thus in specified positions of therotor 14, each of these rods is aligned with teeth 22 of the stator 18.Also, in these alignment positions, the central longitudinal axis Z oftwo opposite teeth 22 of a tooth pair essentially coincides with themagnetic orientation of the appropriate aligned rod. It can also be seenthat the central longitudinal axis M of the coil arrangement 60 isoriented approximately transversely to the direction of motion of therotor 16, and is approximately aligned with the central longitudinalaxis of two mutually opposite teeth of a tooth pair.

Between two adjacent magnetic rods 30 of a stack 14, 14′, to reduce theinert mass of the rotor 16, magnetically inactive, likewise cuboidalspacers 34, 34′ of plastic, e.g. carbon fibre reinforced plastic, areinserted. The mutually adjacent permanently magnetic rods 30 and themagnetically inactive spacers 34, 34′ are permanently connected to eachother. In other words, in the movable part of the actuator (the rotor),there are no parts (e.g. flux concentrating pieces) which conductmagnetic flux, but only permanent magnets, which are always arrangedoptimally in the magnetic field. This arrangement also has the advantageof saving weight. If cuboidal rods of permanently magnetic material arenot available with sufficient magnetic field strength, according to theinvention it is also possible to put the rods together out of permanentmagnet segments, so that a directed (from inside to outside or viceversa) magnetic field transversely to the direction of motion of therotor 16 results.

The stator 18 also has two magnetically conducting outer areas 52, 52′,which are outside the two stacks 14, 14′ of the rotor 16, and because ofthe practically exclusively two-dimensional magnetic flux conduction arepreferably produced as packets of iron sheets. However, it is alsopossible to mould them as soft magnetic moulds of sintered ferrous metalpowder. These outer areas 52, 52′ of the stator 18 are essentiallycomb-shaped in cross-section, and at their ends facing the stacks 14,14′ of the rotor 16 have teeth 22, which in shape correspond to themirror image of the teeth of the inner areas 50, 50 a of the stator 18.

Between the two magnetically conducting inner areas 50, 50 a, there is apredetermined distance A, which is dimensioned so that it essentiallyagrees with the measurement of an even number (two in the shownembodiment) of permanently magnetic rods 30, 30′ of the two stacks 14,14′ (with associated spacers) in the direction of motion B of the rotor16. The length of the outer areas 52, 52′, which are comb-shaped incross-section, of the stator 18 is dimensioned so that the correspondingteeth 22, which face the magnetic rods of the rotor 16, at both ends areopposite a magnetic rod of different orientation. In other words, in aspecified position of the rotor, the teeth 22 of the tooth pair 22 d arealigned with an outwardly oriented magnetic rod, whereas the teeth 22 ofthe corresponding tooth pair 22 c are aligned with an inwardly orientedmagnetic rod. Correspondingly, the teeth 22 of the tooth pair 22 ecorrespond to the teeth 22 of the tooth pair 22 b, and the teeth 22 ofthe tooth pair 22 f correspond to the teeth 22 of the tooth pair 22 a.The outer areas 52 of the stator 18 thus form one magnetic return pathbody. In FIG. 1, the comb-shaped areas of the outer areas 52, 52′ of thestator 18 are illustrated as three individual C-shaped yokes which areplugged into each other. However, it is also possible to form each ofthe two outer areas 52, 52′ of the stator 18 as a packet of one-piecesoft magnetic comb-shaped metal sheets, each of which has the teeth. Anessential advantage of the arrangement according to the invention of theouter area(s) of the stator 18 is that practically no stray magneticflux is output to the environment. This is specially important in thecase of arrangements where multiple such linear actuators are positionedon a dense space, and are driven differently from each other. Thisapplies, for instance, to a multi-valve cylinder of an internalcombustion engine.

For better illustration, in FIG. 3 the stator 18 is shown with its inner50, 50 a and outer areas 52, 52′ exposed. One of the outer areas 52′ andthe upper inner area 50 are omitted. The drawings do not illustrate, butit is within the scope of the invention, that the outer areas 52, 52′ ofthe stator 18 have, in addition to or instead of the inner areas 52 ofthe stator 18, at least one stator coil. Visibly, the measurement of thecoil arrangement 60, 60 a in the direction of motion of the rotor 16 isgreater than the distance between two adjacent tooth pairs of the stator18.

In FIG. 5, a second embodiment of an electrical linear motor 10 isillustrated. The reference symbols which are used in the previousfigures designate parts or components with the same or comparablefunction or method of working, and are therefore explained below only tothe extent that their tangible form, function or method of workingdiffers from what is described above.

In the case of this embodiment, the rotor 16 has a stack 14 of multiplepermanently magnetic rods 30, which arranged one above another and ofessentially cuboidal shape. The stator 18 is in the form of a softmagnetic sheet metal packet stack. The stator 18 has multiple toothpairs 22 a . . . 22 f with mutually opposite teeth 22. Between the teeth22 of a tooth pair, the stack 14 is received, forming an air gap 24 and24′ respectively.

On one side of the stack 14 of the rotor 16 (on the right-hand side inFIG. 5), the stator 18 has two magnetically conducting inner areas 50,50 a, which in the direction of motion B of the rotor 16 are arranged ata predetermined distance A from each other. Each of the two inner areas50, 50 a of the stator 18 is surrounded by an essentially hollowcylindrical coil arrangement 60, 60 a. These two inner areas 50, 50 a ofthe stator 18 practically form the legs of a “U” on its side, itsconnecting yoke being formed by a magnetically conducting outer area52′. In other words, in this embodiment, the second stack of the rotoris omitted, and the stator iron is formed continuously. The outer area52 of the stator 18, outside the rotor 16, is essentially comb-shaped incross-section, and at its end facing the stack 14 of the rotor 16 hasteeth 22, which in shape correspond to the mirror image of the teeth ofthe inner areas 50, 50 a of the stator 18.

In this embodiment too, between the magnetically conducting inner areas50, 50 a, there is a predetermined distance A, which is dimensioned sothat it essentially agrees with the measurement of an even number (twoin the shown embodiment) of permanently magnetic rods 30, 30′ of the twostacks 14, 14′ (with associated spacers) in the direction of motion B ofthe rotor 16. Similarly, the length of the outer areas 52, 52′, whichare comb-shaped in cross-section, of the stator 18 is dimensioned sothat the corresponding teeth 22, which face the magnetic rods of therotor 16, at both ends are opposite a magnetic rod of differentorientation.

The explained embodiments are specially suitable for implementing therequired lift of about 10-200 mm with the required dynamics inrelatively narrow space.

Above, linear actuators for single-phase operation are described.However, it is also within the scope of this invention to form atwo-phase or multi-phase arrangement of the linear actuator. For thispurpose, the teeth of another stator system, with associated coils, mustbe positioned geometrically along the magnet of the rotor, withdisplacement corresponding to the intended phase displacement(s) of theelectrical driving power.

For a person skilled in the art, it is understood that individualaspects or features of the various embodiments described above can alsobe combined with each other. Those skilled in the art also understandthat the terms “armature” and “rotor” are used interchangeably toidentify the moving element 16 in the linear actuator.

In the following claims reference numbers appear only for heuristicpurposes and do not limit the scope of the claims to the referencedelements in the specification.

1. A linear actuator comprising an armature (16) and a stator (18),wherein: the armature (16) having at least two stacks (14, 14′) ofpermanently magnetic rods (30, 30′) arranged one over another; thestator (18) having magnetically conducting inner (50, 50 a) and outer(52, 52′) areas; the stator is at least partly formed of a soft magneticmaterial, has at least one pair of teeth (22 a, 22 a′; 22 b, 22 b′; 22c, 22 c′; 22 d, 22 d′; 22 e, 22 e′; 22 f, 22 f′) with teeth (22)opposite each other; each pair of teeth receiving a stack (14, 14′)between them, forming an air gap (24, 24′); the stator also having atleast two magnetically conducting inner areas (50, 50 a), which at theirends facing the armature (16) have at least one of the teeth (22), andwhich are arranged at a predetermined distance (A) from each other inthe direction of motion (B) of the armature (16), and which are at leastpartially surrounded by a substantially hollow cylindrical coilarrangement (60, 60 a); the hollow cylindrical coil arrangement having acentral longitudinal axis (M) and magnetic flux which are orientedapproximately transversely to the direction of motion (B) of thearmature (16), and at least in sections essentially parallel to thecentral longitudinal axis of two teeth opposite each other of a toothpair; wherein adjacent rods (30, 30′) of a stack (14, 14′) of thearmature (16) have an alternating magnetic orientation (N->S, S<-N), andare essentially aligned with a central longitudinal axis (Z) of twomutually opposite teeth (22) of a tooth pair (22 a, 22 a′; 22 b, 22 b′;22 c, 22 c′; 22 d, 22 d′; 22 e, 22 e′; 22 f, 22 f′); the inner areas(50, 50 a) of the stator (18) are between the stacks (14, 14′) of thearmature (16) and have teeth on their ends facing the stacks (14, 14′);the stator (18) having at least two magnetically conducting outer areaswhich are outside the stack (14, 14′) of the armature (16), and whichhave, at their ends facing the stacks (14, 14′) of the armature (16), atleast one of the teeth; the outer areas (52) of the stator (18) arecomb-shaped and form a magnetic return path body in the direction ofmotion of the armature (16) and are in the form of C-shaped yokes whichare plugged into each other, and each coil arrangement (60, 60 a)completely surrounds the appropriate one of the two inner areas (50, 50a) of the stator (18).
 2. A linear actuator, comprising an armature (16)and a stator (18) wherein: the armature (16) has at least one stack (14,14′) of permanently magnetic rods (30, 30′) arranged one over another;the stator (18) has magnetically conducting inner (50, 50 a) and outer(52, 52′) areas, is at least partly formed of a soft magnetic material,has at least one pair of teeth (22 a, 22 a′; 22 b, 22 b′; 22 c, 22 c′;22 d, 22 d′; 22 e, 22 e′; 22 f, 22 f′) with teeth (22) opposite eachother; each pair of teeth receiving a stack (14) of the armature betweenthem and forming an air gap (24, 24′) which has at least twomagnetically conducting inner areas (50, 50 a), which at their endsfacing the armature (16) have at least one of the teeth (22), and whichare arranged at a predetermined distance (A) from each other in thedirection of motion (B) of the armature (16), and which are at leastpartially surrounded by a substantially hollow cylindrical coilarrangement (60, 60 a); the substantially hollow cylindrical coilarrangement having a central longitudinal axis (M) and magnetic flux ofwhich are oriented approximately transversely to the direction of motion(B) of the armature (16), and at least in sections essentially parallelto the central longitudinal axis of two teeth opposite each other of atooth pair; wherein adjacent rods (30, 30′) of a stack of the armature(16) have an alternating magnetic orientation (N->S, S<-N), and areessentially aligned with a central longitudinal axis (Z) of two mutuallyopposite teeth (22) of a tooth pair (22 a, 22 a′; 22 b, 22 b′; 22 c, 22c′; 22 d, 22 d′; 22 e, 22 e′; 22 f, 22 f′), on one side of the stack(14) of the armature (16); the stator (18) having two magneticallyconducting inner areas (50, 50 a), which are arranged at a predetermineddistance (A) from each other in the direction of motion (B) of thearmature (16), and which have, at their ends facing the armature (16),at least one of the teeth (22); each of the two inner areas (50, 50 a)of the stator (18) is surrounded by an essentially hollow cylindricalcoil arrangement (60, 60 a), a central longitudinal axis (M) andmagnetic flux of which are oriented approximately transversely to thedirection of motion (B) of the armature (16), and at least in sectionsare oriented essentially parallel to the central longitudinal axis oftwo mutually opposite teeth of a tooth pair, wherein the two inner areas(50, 50 a) of the stator (18) form the legs of a “U” on its side, itsconnecting yoke being formed by a magnetically conducting outer area(52′); outer area (52) of the stator (18) disposed outside the armature(16) is essentially comb-shaped in cross-section, and at its end facingthe stack (14) of the armature (16) has teeth (22), which in shapecorrespond to the mirror image of the teeth of the inner areas (50, 50a) of the stator (18), and the outer areas (52, 52′) of the stator (18)are comb-shaped, form a magnetic return path in the direction of motionof the armature, and are in the form of yokes which are plugged intoeach other.
 3. A linear actuator according to claim 1 or 2 wherein thearmature (16) has two or more permanently magnetic rods (30, 30′) whichare arranged in a stack (14, 14′) at a predetermined distance from eachother, and the magnetically conducting inner areas (50, 50 a) of thestator (18) are arranged between the stacks (14, 14′) of the armature(16).
 4. A linear actuator according to claim 2, wherein the hollowcylindrical coil arrangement (60, 60 a) has an essentially rectangularcross-section.
 5. A linear actuator according to claim 4, wherein eachtooth (22) has, in the direction of motion B of the armature (16), ameasurement which essentially agrees with the measurement of apermanently magnetic rod (30, 30′) in the direction of motion B of thearmature (16), so that in a predetermined position of the armature (16),at least one tooth pair of the stator (18) is aligned with a permanentlymagnetic rod (30, 30′).
 6. A linear actuator according to claim 5,wherein in the direction of motion B of the armature (16), adjacenttooth pairs of the stator (18) are dimensioned, relative to themeasurement of the permanently magnetic rods (30, 30′) in the directionof motion B of the armature (16), so that between two permanentlymagnetic rods, which are aligned with two mutually adjacent tooth pairsof the stator (18), at least one other of the permanently magnetic rods(30, 30′) is arranged.
 7. A linear actuator according to claim 1,wherein the predetermined distance A between the magnetically conductinginner areas (50, 50 a) is dimensioned so that it essentially agrees withthe measurement of an even number of permanently magnetic rods (30, 30′)of the two stacks (14, 14′) in the direction of motion B of the armature(16).
 8. A linear actuator according to claim 1, wherein in each case,two adjacent permanently magnetic rods (30, 30′) of the two stacks (14,14′) of the armature (16) are connected to each other by magneticallyinactive spacers (34, 34′), at a predetermined distance.
 9. Linearactuator according to claim 1, wherein because of the measurements ofthe permanently magnetic rods (30) in the direction of motion B of thearmature (16) and the teeth (22) of the stator (18), a pole pitch whichis smaller than the measurement of the stator coil (28) in the directionof motion B of the armature (16) is defined.
 10. Linear actuatoraccording to claim 1, wherein the outer areas (52) of the stator (18)have, in addition to or instead of the inner areas (52) of the stator(18), at least one stator coil (28).
 11. Linear actuator according toclaim 1, wherein the measurement of the coil arrangement (60, 60 a) inthe direction of motion of the armature (16) is greater than thedistance between two adjacent tooth pairs of the stator (18).
 12. Linearactuator according to claim 1, wherein the stator (18) is at leastpartly a soft magnetic mould, preferably of pressed and/or sinteredmetal powder.